- Author: Whitney Brim-DeForest
Over the past year, weedy rice has become a top issue in California rice, both for individual growers and for the industry as a whole. Working together, the University of California Cooperative Extension and the California Rice Commission have come up with a set of tools to assist in getting control of this pest. Of course, none of it would be possible without the input and cooperation of the Pest Control Advisers (PCAs) and California rice growers, who are the first line of defense in dealing with weedy rice. Additional assistance in material development and funding have come from the California Rice Research Board, the California Crop Improvement Association and the staff at the California Rice Experiment Station.
A new website, www.caweedyrice.com, contains all of the most up-to-date information regarding weedy rice in California. The website covers identification, management, and weedy rice sample submission.
An identification pamphlet was mailed out by the California Rice Commission a couple of weeks ago to most growers and PCAs. If you need additional pamphlets, they are available at your local UCCE office. Identification posters will be distributed to Agriculture Commissioner's offices, PCA offices, and rice mills and distributors in each county in the next few weeks. They are also available at your local UCCE office upon request.
The "Weedy Rice Reporter" app will let you send up to six pictures and aGPS location taken with your phone toUCCE RiceAdvisors so that we can confirm or rule out weedy rice. OnlyUCCE RiceAdvisors will be able to access any app submissions. We hope that the app will help us identify infestations early so that management actions can be implemented to eliminate weedy rice from the fields.
- Author: Whitney Brim-DeForest
I went out on a few farm calls in the past week, and have noticed a trend. Due to the unusually wet weather this spring, some of the weeds are already producing seed out in the field! This occurs when the field was moist or wet in the spring, and was not tilled or sprayed prior to planting.
If you have weeds that are already setting seed, follow the steps below:
1) First, make sure to get proper identification of the weed species. Some weed species will produce seed and that seed can germinate and send up a second flush of weeds, in the same season! They are:
- Smallflower umbrella sedge
- Mexican sprangletop
NOTE: There are two types of sprangletop: Mexican and Bearded. Only the Mexican sprangletop will set seed that will germinate this season. Bearded sprangletop seed is dormant and won't germinate until the 2018 season.
2) If you have one of the above-listed species that is already setting seed, it is important to make sure that your follow-up herbicide application will control this second flush of germinating seeds. Otherwise, the amount of seed produced and deposited into the seedbank will be exponentially higher than in a normal year, because there will be two generations of plants that set seed in the same season!
3) If you have a weed species setting seed that is NOT listed above, you will likely not be able to do much this year, as the weeds are likely too large to control with herbicide and any impacts on yield have already occurred. Plan to have an aggressive program for next year (2018)!
I have received reports of significant defoliation due to armyworms from several areas: Glenn, Colusa, Butte and Yolo counties. In most areas the defoliation is severe but the area affected within fields still small.
I inspected a field in Glenn County. The defoliation was severe along levees and in near borders, and worms were about 5th instar. Population was high, similar to 2015.
Severe defoliation along levee.
Severe defoliation along border of field.
Fifth instar armyworms in Glenn County field, 21 June 2017.
The degree day model predicted 5th instar armyworms will start showing up June 22. The heat from last week sped things up, but the model was really close.
Remember that worms feed the most during 5th and 6th instars, and it will take them 10 days to complete their cycle after reaching the 5th instar. This means that there is plenty of time for them to cause more injury and move to other areas of the field. Keep a close eye and consider a treatment if the worms are still present. Do not wait until worms get bigger, they are harder to kill with any insecticide. It's starting to look like 2015./table>
Moth numbers have increased since the week of June 12, specially in the Colusa trap. The degree day model predicted worms in the fifth instar by June 22; I'm starting to receive reports of worms in Colusa, Glenn and Butte counties. Keep your eyes on the field; heat speeds up development and worms may show up earlier.
The number of moths trapped has increased in all locations, except in the North Sutter one (which was already high to begin with). In most fields the rice is still in the three to five leaf stage. In the Colusa and Glenn fields I was able to observe feeding on weeds and rice seedlings on levees that looked like feeding from small armyworms. At the Glenn location, I found very small worms, probably first and second instars, in grassy weeds.
Using a degree day (DD) model developed for the true armyworm, we expect the worms to reach the fifth instar after 255 DD over 50 F, which is when they start feeding voraciously on rice. Using average temperatures for this time of year, that will be in about 10 days. Start monitoring then to make sure you detect infestations early.
You might be wondering, if the worms are already out there, would I benefit from an early insecticide application? Well, maybe yes, maybe not. Those small worms are very susceptible to natural enemies, and many will not make it to fifth instar. There are so many bugs in rice that can feed on those worms, that it might be wise to wait and see if they take care of the population for you./table>